Interactions of nitrogen, phosphorus and potassium fertilization on 'Gala' apple tree nutrition, fruit yield and quality

Interactions between key macronutrient minerals and their effects on micronutrient uptake are likely to influence tree nutrition and fruit yield and quality. This study investigated how different nitrogen (N), phosphorus (P), and potassium (K) application rates affected the uptake and status of mineral nutrients within 15-year-old 'Gala'/M.26 EMLA apple trees (Malus domestica Borkh.) over the 2018-19 growing season. A factorial design of medium or high application rates of N (10 or 50 kg N ha^‑1), P (10 or 40 kg P ha^‑1), and K (50 or 150 kg K ha^‑1) were applied weekly in four equal doses, commencing at four weeks after full bloom (WAFB). Nutrient uptake and leaf nutrient status were monitored by sampling and analysis of leaf petiole and leaf lamina, respectively, at 8, 17, 23 WAFB. Fruit nutrient status, yield, and quality were assessed at fruit harvest at 20 WAFB. Synergistic relationships were observed between K-N treatments and molybdenum (Mo) uptake at 8 WAFB and N-P treatments and zinc (Zn) uptake at 17 WAFB. Antagonistic relationships were observed between Mo uptake and both P-N treatments at 8 WAFB and K-P treatments at 23 WAFB. After 17 WAFB, trees treated with higher N rate had higher leaf N but lower leaf P. Whilst both leaf and fruit boron (B) at harvest increased with high rates of P. The status of other nutrients examined were not affected by the N, P and K rates. This study of only one season did not result in differences in yield and fruit quality.